IANTHINA. 181 



backs, but usually without being able to make a new 

 float ; these fell again heavily to the bottom and soon 

 died. He never saw any swim, like other Gastropods. 

 Clark combated the idea that the float or vesicular mass 

 attached to the foot is a hydrostatic apparatus ; and he 

 asserted that this organ is " the membranous vehicle of 

 the contents of the ovarium and matrix, that has de- 

 scended from under the mantle, and fixed itself to the 

 foot, for a very obvious purpose of the animal economy 

 in reference to the pulli in the genial season." I will 

 not comment on this curious assertion further than by 

 observing that every Ianthina of both sexes, viviparous 

 as well as oviparous, has a float, and that the mode of 

 its construction was fully explained more than a quarter 

 of a century before Mr. Clark wrote. Ianthina can 

 scarcely be considered gregarious, their locomotion 

 being almost involuntary. It is only when driven to- 

 gether by winds or currents that they appear to congre- 

 grate in shoals near coast lines. Some of the old 

 naturalists must have drawn largely on their bank of 

 imagination in making up their accounts of the Ianthina. 

 Born gravely assures us that it lives in the depths of 

 the sea, and in stormy weather rises to the surface, 

 shining with a phosphoric light. I do not know where 

 he got this idle tale. All modern naturalists, who have 

 observed the Ianthina during long voyages, speak of its 

 appearance in fine weather, clotted here and there over 

 the ocean. Dr. Wallich savs that in actual calms it 

 was easy enough to see its floating standard, partly 

 raised above the surface, but at other times it was only 

 by dint of the keenest watching and getting gradually 

 accustomed to detect the outline of the float, that he 

 could distinguish it from the surrounding foam ; and he 

 further remarks that the colour of the shell so nearly 



